U.S. patent application number 10/726141 was filed with the patent office on 2004-07-01 for self-mode locked multi-section semiconductor laser diode.
Invention is credited to Kim, Dong-Churl, Kim, Sung-Bock, Leem, Young-Ahn, Park, Kyung-Hyun, Yee, Dae-Su.
Application Number | 20040125851 10/726141 |
Document ID | / |
Family ID | 32653110 |
Filed Date | 2004-07-01 |
United States Patent
Application |
20040125851 |
Kind Code |
A1 |
Park, Kyung-Hyun ; et
al. |
July 1, 2004 |
Self-mode locked multi-section semiconductor laser diode
Abstract
A multi-section semiconductor laser diode is disclosed. The
laser diode includes a complex-coupled DFB laser section that
includes a complex-coupled grating and an active structure for
controlling the intensity of oscillating laser light, to oscillate
laser light in a single mode, and an external cavity including a
phase control section and an amplifier section, the phase control
section having a passive waveguide that controls a phase variation
of feedback laser light, the amplification section having an active
structure that controls the strength of the feedback laser light.
Currents are separately provided to the three sections to generate
optical pulses with tuning range of tens of GHz. Applications
include the clock recovery in the 3R regeneration of the optical
communication.
Inventors: |
Park, Kyung-Hyun; (Daejeon,
KR) ; Yee, Dae-Su; (Daejeon, KR) ; Kim,
Dong-Churl; (Daejeon, KR) ; Leem, Young-Ahn;
(Daejeon, KR) ; Kim, Sung-Bock; (Daejeon,
KR) |
Correspondence
Address: |
BLAKELY SOKOLOFF TAYLOR & ZAFMAN
12400 WILSHIRE BOULEVARD, SEVENTH FLOOR
LOS ANGELES
CA
90025
US
|
Family ID: |
32653110 |
Appl. No.: |
10/726141 |
Filed: |
December 1, 2003 |
Current U.S.
Class: |
372/97 ;
372/50.22 |
Current CPC
Class: |
H01S 5/34306 20130101;
H01S 5/227 20130101; H01S 5/2206 20130101; H01S 5/06258 20130101;
H01S 5/0265 20130101; B82Y 20/00 20130101; H01S 5/0657 20130101;
H01S 5/1228 20130101; H01S 5/2222 20130101 |
Class at
Publication: |
372/097 ;
372/050 |
International
Class: |
H01S 005/00; H01S
003/082 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 2002 |
KR |
2002-80707 |
Claims
What is claimed is:
1. A self-mode locked multi-section semiconductor laser diode,
comprising: a complex-coupled DFB laser section that includes a
complex-coupled grating and an active structure for controlling the
intensity of oscillating laser light, to oscillate laser light in a
single mode; and an external cavity including a phase control
section and an amplifier section, the phase control section having
a passive waveguide that controls a phase variation of feedback
laser light, the amplifier section having an active structure that
controls the strength of the feedback laser light, the DFB laser
section and the external cavity being monolithically integrated on
a single substrate, current being independently injected into each
of the sections.
2. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the laser diode has a buried
heterostructure.
3. The self-mode locked multi-section semiconductor laser diode, as
claimed in claim 1, wherein the laser diode has a ridge
structure.
4. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the complex-coupled grating of the DFB
laser section is a loss-coupled grating constructed in a manner in
which a diffraction grating is formed in an additional absorptive
layer, which longitudinally periodically varies both effective
refractive index and loss.
5. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the complex-coupled grating of the DFB
laser section is a gain-coupled grating constructed in a manner in
which a diffraction grating is formed in an active structure, which
longitudinally periodically varies both effective refractive index
and gain.
6. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein each of the active structures included
in the DFB laser section and the amplifier section is formed in a
manner in which a first light guiding layer, an active layer, and a
second light guiding layer are sequentially deposited.
7. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 6, wherein each of the first and second light
guiding layers is formed of InGaAsP having a band gap of 1.3 .mu.m
and has a thickness of 70 nm, and the active layer has a
multi-quantum-well structure with a band gap of 1.55 .mu.m
including wells and barriers according to InGaAsP.
8. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 6, wherein each of the first and second light
guiding layers is formed of InGaAsP having a band gap of 1.3 .mu.m
and has a thickness of 70 nm, and the active layer is formed of
InGaAsP having a band gap of 1.55 .mu.m.
9. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the guiding layer of the phase control
section is arranged through butt-coupling such that its central
axis accords with those of the active structures.
10. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 9, wherein the guiding layer has a thickness of
400 nm and is made of InGaAsP having a band gap of 1.3 .mu.m.
11. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the DFB laser section, the phase
control section, and the amplifier section are constructed through
evanescent-coupling in which the sections have a common guiding
layer.
12. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the phase control section is located
between the DFB laser section and the amplifier section.
13. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the amplifier section is located
between the DFB laser section and the phase control section.
14. The self-mode locked multi-section semiconductor laser diode as
claimed in claim 1, wherein the facet of the DFB laser section is
coated with an anti-reflection film, whereas the facet of the
external cavity, opposite to the facet of the DFB laser region, is
coated with a high-reflection film or is left as cleaved.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is based on Korea Patent Application No.
2002-80707 filed on Dec. 17, 2002 in the Korean Intellectual
Property Office, the content of which is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] (a) Field of the Invention
[0003] The present invention relates to a laser diode for
generating frequency-tunable optical pulses, used for 3R
regeneration (re-timing, re-shaping, and re-amplifying) of
restoring an optical signal deformed while being transmitted
through an optical fiber to its original state, and for generation
of high bit-rate optical signals. More particularly, the invention
relates to a self-mode locked multi-section semiconductor laser
diode that can be fabricated on a single substrate and that
includes a complex-coupled DFB (distributed feedback) laser
section.
[0004] (b) Background of the Related Art
[0005] In an optical communication system, an optical signal
transmitted through an optical fiber is subjected to reduction of
its magnitude and temporal deformation due to dispersion while it
is being transmitted. To correct this to restore the optical signal
to its original state, 3R regeneration (re-timing, re-shaping, and
re-amplifying) is required. Among this 3R regeneration, re-timing
is extracting a clock from the deformed signal to obtain a restored
signal from the clock and a deformed optical signal through a
decision element. Methods of extracting the clock include
electrical and optical methods. A. A. Tager published the
theoretical background of generation of optical pulses according to
a short external-cavity laser diode, entitled "High-frequency
oscillations and self-mode locking in short external-cavity laser
diodes" in IEEE J. Quantum Electron, Vol. 30. According to this
article, high-frequency optical pulses can be generated according
to self-mode locking of compound cavity modes. Specifically, this
article discloses that an optical pulse of tens of GHz can be
acquired by self-mode locking of compound cavity modes by
appropriately controlling the light beam strength and phase
variation when a laser beam output from the single-mode laser diode
is propagated through an external cavity and again fed back to the
laser diode in the single-mode laser diode structure including the
short external cavity having a length less than several
millimeters.
[0006] S. Bauer published the self-mode locked DFB laser diode
structure in Electron. Lett. Vol. 38, issued in March of 2002. This
laser diode has an index-coupled DFB laser section and an external
cavity including a phase control section and an amplifier section.
The strength and phase of a light beam, which propagates through
the external cavity and is then fed back to the DFB laser region,
are controlled by injection currents of the amplifier section and
the phase control section, and the injection currents are varied to
obtain a wide frequency tuning range of tens of GHz. However, this
technique may adversely affect the generation of an optical pulse
and stable frequency variation because there is a probability of
occurrence of mode hopping or multi-modes in the index-coupled DFB
laser section according to a feedback phase variation in actual
applications.
SUMMARY OF THE INVENTION
[0007] An advantage of the present invention is to provide a
self-mode locked multi-section semiconductor laser diode including
a single-mode laser section that has no occurrence of mode hopping
or multi-modes even in the event of feedback phase variation.
[0008] In one aspect of the present invention, a self-mode locked
multi-section semiconductor laser diode, comprises a
complex-coupled DFB laser section that includes a complex grating
and an active structure for controlling the intensity of
oscillating laser light, to oscillate laser light in a single mode;
and an external cavity including a phase control section and an
amplifier section, the phase control section having a passive
waveguide that controls a phase of feedback laser light, the
amplifier section having an active structure that controls the
strength of the feedback laser light, the complex-coupled DFB laser
section and the external cavity being monolithically
integrated.
[0009] The sections can be integrated in a way that the waveguide
of the phase control section is arranged through butt-coupling such
that its central axis accords with those of the active structures
of the complex-coupled DFB laser section and the amplifier section,
or in a way that the complex-coupled DFB laser section, the phase
control section, and the amplifier section are constructed in
evanescent-coupling in which the sections have a common guiding
layer.
[0010] The complex-coupled grating may be a gain-coupled grating
formed in an active structure or a loss-coupled grating formed in
an additional absorptive layer, and the laser diode can be
fabricated according to buried heterostructure, ridge structure, or
the like.
[0011] As described above, the laser diode of the present invention
includes the complex-coupled DFB laser section that has a specific
single oscillation mode irrespective of feedback phase variation so
that mode hopping or multi-modes according to feedback phase
variation are not occurred.
[0012] It is to be understood that both the foregoing general
description and the following detailed description of the present
invention are exemplary and explanatory, and are intended to
provide further explanation of the invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this application, illustrate embodiment(s) of
the invention, and together with the description serve to explain
the principle of the invention. In the drawings:
[0014] FIG. 1 illustrates the structure of a self-mode locked
three-section semiconductor laser diode according to the present
invention; and
[0015] FIG. 2 is a cross-sectional view of FIG. 1 taken along the
line indicated by the arrow X.
DETAILED DESCRIPTION OF THE INVENTION
[0016] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings.
[0017] FIG. 1 illustrates a self-mode locked three-section
semiconductor laser diode having a buried heterostructure and
including a loss-coupled DFB laser section according to the present
invention.
[0018] Referring to FIG. 1, the present invention comprises an
external cavity EC including a phase control section P and an
amplifier section A, and a DFB laser section DFB. A complex-coupled
grating 2 is located on an n-InP substrate 1. The area of the
grating corresponds to the DFB laser section DFB. An n-InP layer 3
having a thickness of 100 nm approximately covers the grating 2.
The complex-coupled grating 2 is formed of InGaAs having a bandgap
wavelength of longer than 1.55 .mu.m so that loss is longitudinally
and periodically varied as well as an effective refractive index.
That is, the complex-coupled grating 2 is a loss-coupled grating,
but the DFB laser section may have any kinds of complex-coupled DFB
laser structure.
[0019] An active structure S of a separate confinement
heterostructure (SCH) made of a first guiding layer 4, an active
layer 5, and a second guiding layer 6 is formed only at the portion
corresponding to the DFB laser section DFB and the amplifier
section A. Each of the first and second guiding layers 4 and 6 has
a thickness of 70 nm, and is formed of InGaAsP having a band gap of
1.3 .mu.m. The active layer 5 has a multi-quantum-well structure
with a band gap of 1.55 .mu.m, which includes wells and barriers
made of InGaAsP.
[0020] A guiding layer 7 is formed in close proximity to the n-InP
substrate 1 at the region interposed between two active structures
S, corresponding to the phase control section P. The guiding layer
7 is formed of InGaAsP having a band gap of 1.3 .mu.m and has a
thickness of 400 nm. The guiding layer is butt-coupled with the
active structures S such that the central axis of the guiding layer
accords with those of the active structures.
[0021] Current blocking layers B, each of which is formed in a
manner such that a p-InP layer 8, an n-InP layer 9, and a p-InP
layer 10 are sequentially deposited, are provided on both sides of
the active structure S and the guiding layer 7 having a width of
about 1 .mu.m.
[0022] Moreover, a p-InP clad layer 11 is deposited on the guiding
layer 7, on the active structures S placed at both sides of the
guiding layer 7, and on the current blocking layers B. A p-InGaAs
layer 12 having a thickness of 300 nm is formed on the p-InP clad
layer 11, to reduce contact resistance with a metal film E2. A SiNx
film 13 having an opening for injection current is coated on the
p-InGaAs layer 12, and the metal layer E2 is formed on the SiNx
film 13 including the opening. A metal film E1 is formed beneath
the n-InP substrate 1. The metal films E1 and E2 serve as
electrodes. As shown in FIG. 2, the amplifier section A, phase
control section P, and DFB laser section DFB are electrically
separated from one another according to a groove 14 having a width
of about 10 .mu.m so that neighboring sections have a resistance of
greater than several hundreds of .OMEGA. between them.
[0023] In this embodiment, the DFB laser section DFB, phase control
section P and amplifier section A have lengths of 300 .mu.m, 400
.mu.m, and 200 .mu.m, respectively. Although the three sections are
arranged in the order of the DFB laser section DFB, phase control
section P, and amplifier section A in this embodiment, they can be
arranged in the order of the DFB laser section DFB, amplifier
section A, and phase control section P.
[0024] The facet of the DFB laser section DFB is coated with an
anti-reflection film F, whereas the facet of the amplification
section A, opposite to the facet of the DFB laser section, is left
as cleaved or coated with a high-reflection film.
[0025] The three sections DFB, P, and A are provided with direct
current independently. Specifically, a current higher than a
threshold current value is applied to the DFB laser section DFB so
that the laser diode oscillates in a single mode. The oscillated
laser beam propagates to the external cavity formed according to
the phase control section P and amplifier section A, and then it is
fed back to the DFB laser section DFB. Here, the strength and phase
variation of the feedback beam are controlled by the injection
currents applied to the amplifier section A and phase control
section P. When the strength and phase variation of the feedback
light are appropriately adjusted, an optical pulse of tens of GHz
is generated according to self-mode locking of compound cavity
modes. Also, the frequency of the optical pulse can be varied by
controlling the strength and phase variation of the feedback
beam.
[0026] Furthermore, the present invention uses the complex-coupled
DFB laser section, which is different from an index-coupled DFB
laser section, so that a specific single mode oscillates all the
time irrespective of a phase variation of feedback beam. Thus, the
frequency of the optical pulse is stably varied.
[0027] Moreover, when an optical signal of a wide range of rates
that has been deformed while being transmitted is applied to the
laser diode of the present invention, optical clock signals
corresponding to the rate of the optical signal can be extracted
according to injection locking. Accordingly, the laser diode can be
used for clock recovery in a 3R regeneration.
[0028] The foregoing embodiments are merely exemplary and are not
to be construed as limiting the present invention. The present
teachings can be readily applied to other types of apparatuses. The
description of the present invention is intended to be
illustrative, and not to limit the scope of the claims. Many
alternatives, modifications, and variations will be apparent to
those skilled in the art.
[0029] The present invention uses a complex-coupled DFB laser
section that has a specific single oscillation mode all the time,
so that a feedback phase variation cannot affect the single-mode
oscillation to create mode hopping or multi-modes. Furthermore,
since the external cavity composed of the amplifier section and
phase control section can control the strength and phase variation
of a beam fed back to the DFB laser section, an optical pulse whose
frequency can be stably varied within a wide range can be
generated. Accordingly, the laser diode of the invention can be
used for data transmission in ultra-high-speed optical
communications.
* * * * *